Theresa May wants an early deal on the status of Britons living in the EU and European citizens in the UK after Brexit.
The Prime Minister addressed the other 27 European Union leaders amid concern from many of them about the rights of their nationals in the UK after Brexit.
Irish Taoiseach Enda Kenny revealed the PM's comments after the European Council summit meeting in Brussels.
He told reporters: "She would like to have the question of UK citizens living in Europe and European citizens living in the UK dealt with in the early part of discussions that take place."
Mr Kenny's comments came after Mrs May left the summit in Brussels without answering any questions on the UK's break from the EU.
Mr Tusk said representatives of the European Parliament would be invited to preparatory meetings but "maybe it's not enough" to placate the angry MEPs.
Outgoing European Parliament president Martin Schulz has warned negotiations could be vetoed if MEPs are not fully involved, resulting in the "hardest Brexit possible".
Meanwhile, Downing Street insisted the Brexit process could be completed within two years after the UK's ambassador to the EU privately warned it could take a decade to finalise and even then may fail to be ratified by member states.